﻿#define _CRT_SECURE_NO_WARNINGS
// 29求斐波那楔数.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include <stdio.h>
//1 1 2 3 5 8 13 21....
int Fib(int n)
{
   
    if (n <= 2)

        return 1;
    else return Fib(n - 1) + Fib(n - 2);
    
}
int main()
{
    int n = 0;
    int ret = 0;
    //scanf("%d", &n);
    //ret = Fib(n);
    int m = 0;
    int i = 0;
    int sum = 0;
    scanf("%d", &m);
    for (i = 1; i <=m; i++)
    {
        sum = sum + Fib(i);
    }
    printf("ret=%d\n", sum);
    //printf("count=%d\n", count)
        return 0;

    return 0;
}

